Disambiguating grappling: Push-pull tangle as an intriguing social interaction in spider monkeys

Until now, the term grappling described three different social interactions in spider monkeys (Ateles spp.): a form of wrestling play, a form of aggressive interaction involving agonistic behaviours, and a complex, non-aggressive interaction involving several behavioural elements including face touching, embracing, and genital touching, but not play. Given this ambiguity, we focused on documenting the behavioural elements involved in the latter form and rename it as "push-pull tangle" based on its behavioural dynamics to distinguish it from the other two forms. We carried out observations on two species of spider monkeys, in the wild and in a zoo setting. We observed individually identified Geoffroy's spider monkeys living in the Otoch Ma'ax yetel Kooh protected area, Yucatan, Mexico. We observed Colombian black-faced spider monkeys at Chester Zoo, United Kingdom. At both sites we recorded details about push-pull tangle ad libitum. We observed 13 bouts of push-pull tangle during approximately 800 h in Mexico and 12 bouts during approximately 300 h at Chester Zoo. Consistent behavioural elements occurred across the two species including face greeting, face touching, body sniffing, mutual embraces, tail wrapping, straddling of the partner, and touching the partner's genitals. The bouts of push-pull tangle were long lasting. Given none of the observed bouts were associated with either aggression or play when both participants were adults, it warrants being renamed as push-pull tangle to disambiguate it from the other two forms of grappling.